Preformed dental constructs may be produced in various forms, including crowns, veneers, inlays, onlays and false teeth. They may be constructed from a variety of materials, such as, ceramics, glass-ceramics, glass, porcelain, porcelain-fused-to metal (PFM), and organic materials.
Glass-ceramics found useful in producing dental constructs are described, for example, in U.S. Pat. Nos. 3,732,087 (Grossman) and 4,431,420 (Adair). These patents disclose tetrasilicic fluormica glass-ceramics having properties particularly suited to producing such articles.
As described in the patents, a molten glass is cast in a mold by a process known as investment casting. The resulting glass construct is then thermally converted to a glass-ceramic. Normally, the construct is translucent and uncolored, but colorants may be included in the glass compositions, if desired.
Recently, a new system for the manufacture of crowns and other dental constructs has been proposed. This alternative to prior casting methods involves utilizing CAD/CAM techniques to provide computer-controlled milling of a solid block to a prescribed contour. Typical systems are described, for example, in European Patent Application 0/311/214/A1 (van der Zel) and U.S. Pat. No. 4,575,805 (Moermann et al.).
The present invention is particularly convenient to use with constructs prepared by this technique, but is not so limited. Rather, it is applicable to dental constructs by whatever manner produced and from whatever material employed.
While uncolored dental constructs are technically satisfactory, appearance frequently demands coloration for cosmetic effect. It is, of course, possible to include colorants in an original glass melt, as suggested in the Grossman and Adair patents. This provides a uniform coloration which may be acceptable for such purposes as small fillings or inlays.
For larger restorations, such as veneers, crowns and onlays, a more sophisticated system of coloration is desired. For example, color gradation from the neck of a crown to the incisal edge would be desirable. Also, special effects whereby the restoration would blend with the surrounding dentition could be very useful.
This desire for variable color effects has led to a search for a surface coloration technique. One such procedure is disclosed in U.S. Pat. No. PG,4 4,650,418 (Blair et al.). In this process, multiple layers of colored porcelain glazes are successively fired onto the outside surface of a restoration. In this way, distribution of color across the surface, as well as in depth, can be varied.
The process is effective, but requires a degree of artistic talent to arrange colors for a natural effect. Thus, a technician may use a brush to place or flow a wet porcelain glaze mixture where needed. It would, obviously, be desirable to provide a simpler procedure that requires less skill in application.